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Topic: Question 386 block (Read 3963 times)

HIIt might seem like a silly question for some of you, I have a 69 327 with a 386 casting. If this is the same casting # as early dz & 350 engines, why do 302 & 350 use different motor frame mounts than the 327 ? Thanks

John may be able to answer specifics as to the desygn/why question, but until he replies, one can only suppose that the designers felt a need to supply a different mount for higher performance engines. This is independent of the block casting. If you swapped the brackets as well, you should be able to put a bracket/mount combo from a 302 or 350 onto a 327 block.

Same casting - 2 bolt main variant as opposed to the 4 bolt main used for the higher hp engines. What always boggled my mind about this is that building both 2 bolt and 4 bolt engines out of the same block had to have created additional part and inventory control issues for Chevrolet / GM with regard to usage. One would have thought the block would have been machined the same for all builds (302, 327, or 350 usage) and simply change the internals as required to build the correct displacement. But they didn't. Although one could argue additional machining time to bore and drill the extra holes, this doesn't make sense to me either in that I suspect that all of those drill and tapping machining steps were all automated and done at the same time. However, someone had to keep up with and make sure that the 2 bolt main blocks went where they were supposed to go and likewise for the 4 bolt main blocks. Had to be some additional manual labor hours there.

The 327 in my '69 RS is a 386 block, assembled at the Flint engine plant on 11/22/68. It is a 2 bolt main block - as were all 327 engines built by Chevy.

I get confused myself about the various combinations of frame brackets and mounts for different small-block engines, and can never remember it - I usually wait for William to chime in and explain it. I don't know why they're different, unless it has something to do with clearance to the front stabilizer bar with 7" vs. 8" balancers.

The extra six main cap bolt holes in 4-bolt blocks were drilled and tapped in the main block machining transfer line, but those six holes were done in a separate station in the line; there wasn't room for the six 4-bolt tool-head spindles next to the 2-bolt hole spindles. The 4-bolt blocks were easily detected after that station by automatic probes in subsequent stations - no manual intervention was required. There was no difference at all in the block casting between 4-bolt and 2-bolt blocks - some got ten main cap holes drilled/tapped, some got sixteen.

HIIt might seem like a silly question for some of you, I have a 69 327 with a 386 casting. If this is the same casting # as early dz & 350 engines, why do 302 & 350 use different motor frame mounts than the 327 ? Thanks

One of the first and largest auto recalls back in the '60s was caused by failure of the LH motor mount in 8 cylinder '65-'68 Chevrolet passenger cars. When the mount failed, under acceleration the engine would lift off the bracket, often causing the accelerator linkage to bind. The car would continue accelerating even after releasing pressure on the fuel pedal.This caused several serious accidents. The recall involved the band-aid fix of a cable/bracket assembly attached to the exhaust manifold and looped around the upper control arm shaft.

For '69 Chevy re-designed the mount with an integral hook to prevent physical separation of the parts if the rubber/metal bond failed. The "interlock" mount was narrower and thicker than the previous design necessitating re-designed frame brackets. For sb '69 Camaros Chevy only used the new mount/brackets with 302 and 350 engines, deemed most likely to need them. 307 and 327 engines continued to use the old design.

The problem with this is the early mount will fit the later interlock frame bracket. It is a very sloppy fit; the engine will be positioned too low and can easily move around causing clutch chatter and driveline vibration.